There has been a two-stage air-conditioning apparatus including a first refrigeration cycle at a high level and a second refrigeration cycle at a low level, and having an intermediate heat exchanger for exchanging heat between refrigerants, which circulate through the respective refrigeration cycles, counter to one another (for example, see Patent Literature 1). In a technology described in Patent Literature 1, zeotropic refrigerant mixtures having different temperature glides are employed for the refrigerants, which circulate through the respective first and second refrigeration cycles.
Also, there has been suggested an air-conditioning apparatus that controls the condensing temperature and the evaporating temperature of a refrigerant in consideration of a phenomenon in which the circulation composition of the refrigerant is changed in accordance with the amount of the liquid refrigerant stored in an accumulator, and hence that can increase heat exchanging efficiency (for example, see Patent Literature 2).
Further, there has been suggested a multi-air-conditioning apparatus for a building (for example, see Patent Literature 3). The multi-air-conditioning apparatus includes a first refrigeration cycle and a second refrigeration cycle, and can generate hot water by exchanging heat between refrigerants, which circulate through the respective first and second refrigeration cycles.